a) For a while. These cells don't have much capacity. Also expect the output to drop quite a bit with low temps at altitude. You would probably be better off with something like 3x CR123 lithium cells in series.
b) It is not critical. 22 Ga. hookup wire will be fine.
c, d) A breadboard is good for prototyping and testing. But not so robust for flight. I would recommend transferring your circuit to a "PermaProto" board and soldering all connections. https://www.adafruit.com/index.php?main ... permaproto
e) GPS and pressure measurements should be fine (you may want to make sure there are some pin-holes to allow the pressure to equalize) Temperature measurements may be off due to the insulating value of the foam and the heat generated by the electronics.
f) Double-sided foam tape usually works well. Avoid covering the opening on the pressure sensor.
The wiring will just be a combination of the diagrams in the tutorials. I can try to sketch up a combined diagram later this afternoon.